Thunder Bay's Remedial Action Plan group now knows more about the contaminants that lay at the north end of the city's harbour.

The consultant hired by the group looked into the area beside the former Thunder Bay Fine Papers mill and reported on some of the findings at a meeting Wednesday night.

For decades, the mill's effluent discharged into Lake Superior had fine particles of paper that contained some mercury.

Those particles now spill out a distance from shore, with some areas having paper sludge that measures more than a metre in thickness.

An environment Canada spokesperson said wind currents and even boats can disturb what she calls "fluff" on the top of the sludge.

"We were out doing sampling a few years ago and, after our barge went by, there was a huge plume of suspended particles," Kay Kim said.

Study focuses on north end of harbour

One of the report’s authors said the good news is there's virtually no danger to the public eating fish from this part of the harbour.

"If you looked at the fish you might catch on any given day, really there is no risk [to human health]," Susan Winch said.

Winch noted the bigger challenge now is to cap the sludge, so it can't move up the food chain, from plants to fish.

One of the report’s co-authors noted the study focused only on the north end of the harbour.

"That's the area where we're seeing the highest … concentrations of mercury," Adam Dawesaid.

"[That’s where] we're having the greatest… impact on the overall local ecosystem.